The present invention relates to an optical element positioning apparatus that performs positioning of an optical element suitable for, for example, an exposure apparatus used in a lithography process of a device manufacturing process.
Semiconductor devices, such as semiconductor memories and logic circuits with a minute circuit pattern, are manufactured using a photolithography (exposure) technique. For this purpose, conventionally, a reduction projection exposure apparatus is used. The reduction projection exposure apparatus projects a circuit pattern drawn on a reticle (or mask) through a projection optical system onto a substrate, such as a wafer, to transfer the circuit pattern thereon.
A minimum dimension (resolution) transferable with the reduction projection exposure apparatus is proportional to a wavelength of light used for exposure, and inversely proportional to a numerical aperture (NA) of the projection optical system. Accordingly, a shorter wavelength results in a higher resolution. Consequently, in order to satisfy the recent need for miniaturization of semiconductor devices, the wavelength of the exposure light is being reduced. For example, as a light source of ultraviolet light, an ultra-high pressure mercury lamp (i-ray (wavelength: approximately 365 nm)), a KrF excimer laser (wavelength: approximately 248 nm) or an ArF excimer laser (wavelength: approximately 193 nm) is used.
However, since the miniaturization of semiconductor devices is progressing rapidly, there is a limit in the lithography using ultraviolet light. In order to efficiently transfer extremely minute circuit patterns on the order of 0.1μ or less, a reduction projection exposure apparatus, which uses an extreme ultraviolet ray (EUV) (hereafter, referred to as an EUV exposure apparatus), has been developed. The wavelength of the extreme ultraviolet ray (EUV) is approximately 10 to 15 nm, which is further shorter than that of the ultraviolet light.
To achieve a high resolution exposure, the position and posture of optical elements, such as mirrors and lenses located within the projection optical system, have to be precisely measured, and the optical elements have to be positioned so that the wavefront aberration falls within a permissible value. To precisely measure the position and posture of the optical elements, for example, laser gauge interferometers, mounted on a measuring frame, whose installation surfaces are satisfactorily prevented from vibrations and which has a satisfactory rigidity, are desirably used. However, due to the actual disposition of the laser gauge interferometers, it is extremely difficult to measure the position and posture of the optical elements disposed within an optical element holding barrel of the projection optical system, from such a measuring frame.
Japanese Patent Laid-Open No. 2005-175177 discloses a method in which laser gauge interferometers are mounted on an optical element holding barrel, and the movement amount of optical elements (mirrors) is measured.
Japanese Patent Laid-Open No. 2006-250587 discloses a measuring apparatus in which first and second sensors are provided, whose measurement axes are previously adjusted in a first axial direction and a second axial direction, respectively. The measuring apparatus is provided with the first and second sensors (three for each) between an inner ring and an outer ring. Thereby, relationships in positions and postures of the inner ring and the outer ring in directions of X, Y, Z, θx, θy, θz are calculated.
When the laser gauge interferometers are mounted on the optical element holding barrel as disclosed in Japanese Patent Laid-Open No. 2005-175177, mounting errors of the laser gauge interferometers cause Abbe errors, which cause errors in measurement results of the movement amounts of the mirrors. To reduce the measurement errors due to the mounting errors of the laser gauge interferometers, the positions of the laser gauge interferometers mounted on the optical element holding barrel and the spans between the laser gauge interferometers have to be precisely obtained. However, it is extremely difficult to precisely obtain the positions of the laser gauge interferometers mounted on the optical element holding barrel and the spans therebetween.
Even when the measuring apparatus is used, in which the first and second sensors, whose measurement axes are previously adjusted in the first and second axial directions, as disclosed in Japanese Patent Laid-Open No. 2006-250587, a measurement error caused from the mounting error of the measuring apparatus cannot be prevented.